The drawing of diagonal or oblique lines may next be practised, as in Fig. 4. In all these examples, the board or slate should never be moved or reversed; the end forming the topmost one should always remain so. We are aware that some parties have greater facilities for drawing lines in one direction than in another; thus, the majority of beginners would draw lines sloping from right to left with much more ease than in the reverse position. We have seen cases where, in lessons like the foregoing, the lines sloping from right to left were drawn first, the board reversed, and lines to represent those sloping the reverse way drawn in the same direction exactly; the board was then turned to its original position, when the sets of lines appeared sloping different ways, while, in reality, they were done both in the same manner. This practice is not honest either to the teacher or pupil, and should at once be discarded.
The examples now given have had reference only to one peculiar position of the lines to be drawn; that is, they have all been horizontal, or all perpendicular or oblique; placed in the same relative position to one another. We now give an example where the lines go in different directions with respect to one another. Thus in drawing the lines _b a_, _a f_, _d c_, and _c e_, Fig. 5, care must be taken to have the lines perpendicular to one another; that is, supposing the lines _a b_, _c d_, to be drawn first, the horizontal lines _a f_, _c e_, must be drawn so that the points or ends _f e_ shall be neither above nor below the ends or points _a_, _c_--that is, _f_ and _e_ must be exactly opposite _a_ and _c_. In the present case, no mechanical aid is allowable; the eye is to be the only guide. Attention should also be paid to keeping the exact distance between the lines _a b_, _a f_, and _c d_, and _c e_. The pupil must not imagine that all these modifications of lines are worthless; a little patience and reflection will suffice to show him that they are, in truth, part of the groundwork, without which he can never hope to rear the superstructure of perfect drawing. We now proceed to a little more interesting labor, where simple figures are to be drawn; these, however, being neither more nor less than the lines already given variously disposed. Draw the lines _a c_, _b c_, Fig. 6, meeting in the point _c_; these form a certain angle; care should be taken to draw the lines as in the copy. Next draw the horizontal line _a b_, Fig. 7, and a figure is formed which the pupil will at once recognize. Draw the horizontal line _a b_, Fig. 8; perpendicular to it, from the ends _a b_, draw the lines _a c_, _b d_, taking care that they are of the same length as _a b_; draw the line _c d_, a square is at once formed. As it is an essential feature in this form that all the sides are equal, if the pupil, after drawing it, perceives any inequality therein, he should rub it out and proceed to another attempt. Some little practice should be given to the delineation of squares, angles, &c. If a parallelogram or oblong--vulgarly called an oblong square--is wished to be drawn, it may be done by making two opposite lines shorter than the others; the line _e_ denotes the fourth outline of an oblong, of which the side is _a b_. If two oblongs be drawn, care being taken to have the inner lines the same distance within the outer ones all round, by adding a narrow line outside these, as in Fig. 9, the representation of a picture-frame is obtained; the diagonal lines at the corners, as at _a_ and _b_, being put in to represent the joinings at the corners of the frame, the "mitre" joints, as they are termed. By first drawing the simple outlines, as in Fig. 10, the foundation of a door is obtained by filling in the extra lines, as in the figure.